Fuel cell start up method

ABSTRACT

A fuel cell module is configured or operated, or both, such that after a shut down procedure a fuel cell stack is discharged and has its cathode electrodes at least partially blanketed with nitrogen during at least some periods of time. If the fuel cell module is restarted in this condition, electrochemical reactions are limited and do not quickly re-charge the fuel cell stack. To decrease start up time, air is moved into the cathode electrodes before the stack is re-charged. The air may be provided by a pump, fan or blower driven by a battery or by the flow or pressure of stored hydrogen. For example, an additional fan or an operating blower may be driven by a battery until the fuel cell stack is able to supply sufficient current to drive the operating blower for normal operation.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent claims the benefit of U.S. provisional patent applicationNo. 61/619,073 filed on Apr. 2, 2012 which is incorporated herein byreference.

FIELD

The invention relates to fuel cells, and, in particular to a method andapparatus for restarting a fuel cell.

BACKGROUND

A fuel cell converts chemical energy stored in a fuel into a useful formof energy, such as for example, electricity. One example of a particulartype of fuel cell is a Proton Exchange Membrane (PEM) fuel cell that isoperable to produce electricity.

A typical PEM fuel cell includes an electrolyte membrane arrangedbetween an anode electrode and a cathode electrode. Hydrogen fuel issupplied to the anode electrode and an oxidant is supplied to thecathode electrode. Within the PEM fuel cell the hydrogen fuel and theoxidant are employed as reactants in a set of complementaryelectrochemical reactions that yield electricity, heat and water.

A number of factors cause other undesired reactions to occur thatincrease the rate of wear and degradation experienced by some componentsof a PEM fuel cell. For example, small amounts of hydrogen fuel andoxidant remaining inside a PEM fuel cell, after respective supplies ofthese reactants are closed off, are known to combust during shutdown andrestarting processes. Combustion within a PEM fuel cell causes thedeterioration of various components including the electrolyte membraneand catalyst layers deposited on the electrodes. The cumulativedeterioration of various components significantly reduces the efficiencyof the PEM fuel cell and may lead to failure of the PEM fuel cell.

More specifically, combustion as opposed to electrochemical consumptionof the hydrogen and oxygen occurs because the conditions within a PEMfuel cell module start to change as support systems operable during thenormal operation (i.e. the on state) of the PEM fuel cell module areswitched to an “off” state. As the internal conditions change, somehydrogen molecules diffuse to the cathode side of the membrane and burnin the presence of the oxygen. Similarly, some oxygen molecules diffuseacross the membrane and react with the hydrogen fuel on the anode sideof the membrane. The diffusion of hydrogen across the membrane isactually more common (in the absence of a driving differential pressureacross the membrane) since hydrogen molecules are smaller than oxygenmolecules, and, thus more readily diffuse through the membrane.

Another undesired reaction that may occur is the electrochemicalcorrosion of at least one catalyst layer within a PEM fuel cell. Thisfurther deteriorates the performance of a PEM fuel cell.

U.S. Pat. No. 7,425,379 B2, entitled Passive Electrode Blanketing in aFuel Cell and issued on Sep. 16, 2008, describes a fuel cell modulehaving a fuel cell stack, a parasitic load connectable across theelectrodes, and a reactant reservoir for storing an amount of a firstreactant such as hydrogen. When the fuel cell module is shutdown, thestored amount of the first reactant can be drawn to react with an amountof a second reactant (e.g., oxygen in air) remaining in the stack toelectrochemically consume the first and second reactants, therebyleaving a mixture that substantially comprises a non-reactive agent(e.g., nitrogen), thereby passively blanketing the electrodes. Theparasitic load limits the voltage of the fuel cell stack and induces theelectrochemical consumption of the first and second reactants remainingin the stack during shutdown. A pressure gradient between the electrodesand an optional check valve may allow for movement of the non-reactiveagent between electrodes. A process related to said fuel cell module isalso provided.

INTRODUCTION TO THE INVENTION

The following discussion is intended to introduce the reader to thedetailed description to follow, and not to limit or define any claimedinvention.

The inventor has observed that a fuel cell that has been blanketed witha non-reactive agent, for example a fuel cell that has been shut down asdescribed in U.S. Pat. No. 7,425,379 B2, can require varying amounts oftime to restart. For example, a fuel cell that has been shut down foronly a minute, and a fuel cell that has been shut down for a day ormore, tend to restart essentially immediately. A fuel cell that has beenshut down for an hour, however, may take longer to restart. The delayedstart is less noticeable when a battery, typically provided to operatevalves and electronic controls while the fuel cell stack is notoperating, is sufficiently large. However, it is generally desirable toreduce the size of the battery to the extent possible.

When a fuel cell module is shut down, its fuel cell stack is typicallyleft in a discharged state to, among other reasons, avoid presenting anunsuspected electrical hazard. Without intending to be limited bytheory, it is possible that at some periods of time following a shutdown with passive electrode blanketing, the cathode electrodes of thefuel cell stack are so completely blanketed with nitrogen that there isvery little, if any, oxygen available to the cathode electrodes.Electrochemical reactions are correspondingly limited, or not available,and so do not quickly electrically re-charge the fuel cell stack whenthe fuel cell module is restarted. A similar problem might occur in afuel cell stack that was blanketed with a non-reactive agent by way ofsome other process.

A process and apparatus are described herein to introduce oxygen to thecathode electrode of a fuel cell stack during start up. While a fuelcell module typically has a blower adapted to supply air to the cathodeduring operation, this operating blower is sized to provide sufficientair for the maximum power output of the fuel cell stack and is typicallypowered by the fuel cell stack after the fuel cell stack has beenre-charged. The process and apparatus provide a lesser flow of oxygen,but at a reduced power requirement. This lesser flow of oxygen can bepowered or instigated by a battery before the fuel cell stack isrecharged.

A fuel cell module is described herein having a fuel cell stack with adevice to supply a reactant (e.g., oxygen in air) to one or more cathodeelectrodes. The device, such as a fan, a pump or the operating blower,is operable by way of an electrical input provided by a battery beforethe stack is charged, by pressure energy, or both. For example, butwithout limitation, the device may be a fan provided in fluidcommunication with a cathode electrode. The fan is provided in additionto an operating blower used to supply air to the fuel cell stack afterstart up, and has a lower threshold power requirement than the operatingblower. Optionally, the fan may be used as a flow meter when the bloweris operating. In an alternative module, a circuit is provided thatallows the battery to turn the operating blower at low speed for aperiod of time, for example until the fuel cell stack is recharged.

A process for starting a fuel cell module is described herein. Theprocess has a step of providing a flow of oxygen to a cathode electrodebefore the fuel cell stack is charged or without using power produced bythe fuel cell stack. The cathode electrode may have been previouslyblanketed with a non-reactive agent. Optionally, the flow of oxygen maybe provided or instigated by an electrical device driven by a battery.

In one fuel cell module described in the detailed description, there is:a fuel cell stack including at least one fuel cell, each fuel cellincluding an anode electrode, a cathode electrode and an electrolytemedium arranged between the anode electrode and the cathode electrode,wherein during normal operation the anode electrode is provided with afirst reactant and the cathode electrode is provided with a firstmixture containing a second reactant and a non-reactive agent; aparasitic load that is connectable across the anode and the cathodeelectrodes; a reactant reservoir, connectable to the anode electrode,and able to store an amount of the first reactant suitable for ashutdown process of the fuel cell module, whereby, in use when the fuelcell module is shutdown, the stored amount of the first reactant isdrawn from the reactant reservoir and electrochemically reacts with anamount of the second reactant remaining in the fuel cell module, toelectrochemically consume some or all of the amounts of the first orsecond reactants, or both, thereby leaving a second mixture thatsubstantially comprises the non-reactive agent; and a fan, pump orblower connected or connectable to the cathode electrode and operable tosupply the first mixture to the cathode electrode while the fuel cell isnot charged. The reactant reservoir may be, for example, a separate tankor piping used to provide the first mixture during ordinary operation ofthe fuel cell module. The reactant reservoir may be sized, or may bere-fillable, such that an amount of the first reactant, in addition tofirst reactant remaining in the fuel cell stack on shutdown, may beprovided to electrochemically consume the amount of the second reactantremaining in, and drawn into, the fuel cell module during the shutdownprocess. The fuel cell module also has a means for providing, during arestarting procedure, more of the fixed mixture to the cathode electrodeusing a source of power other than the fuel cell stack, for exampleuntil the fuel cell stack is charged.

In one process described in the detailed description, for shutting downand re-starting a fuel cell, the fuel cell including a first electrode,a second electrode and an electrolyte membrane arranged between thefirst and second electrodes, wherein during normal operation the firstelectrode is provided with a first reactant and the second electrode isprovided with a first mixture containing a second reactant and anon-reactive agent, the process comprises: stopping an inflow of thefirst reactant into the first electrode; cutting-off power to supportingbalance of plant elements; drawing current through a parasitic loadconnectable across the first and second electrodes; providing an amountof a first reactant for the electrochemical consumption of a remainingamount of a second reactant; permitting a delayed inflow of an amount ofthe first mixture into the second electrode, optionally wherein theamount of the first reactant and first reactant remaining in the fuelcell stack on shutdown electrochemically react with the remaining andinflowing amounts of the second reactant, thereby leaving a secondmixture that comprises the non-reactive agent; and, to re-start the fuelcell module, providing a flow or amount of the first mixture before thefuel cell stack is re-charged or by power drawn from a source other thanthe fuel cell stack.

Other aspects and features of the present invention will becomeapparent, to those ordinarily skilled in the art, upon review of thefollowing description of one or more examples or processes andapparatus. The examples are intended to include at least one embodimentof every claim, but every example is not necessarily an embodiment ofevery claim, and every claim does not necessarily include every example.The examples may also include features that are not steps or elements ofany claim.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram of a fuel cell module;

FIG. 2 is a schematic diagram illustrating a first arrangement of a fuelcell module;

FIG. 3 is a chart illustrating the composition of gases present incathode electrodes of the fuel cell module shown in FIG. 2 duringsequential stages of a shutdown process;

FIG. 3B is a chart illustrating the composition of gasses present incathode electrodes of the fuel cell module shown in FIG. 2 duringsequential stages of a start up process;

FIG. 4 is a schematic diagram illustrating a second arrangement of afuel cell module;

FIG. 5 is a schematic diagram illustrating a third arrangement of a fuelcell module; and

FIG. 6 is a schematic diagram illustrating a fourth arrangement of afuel cell module.

DETAILED DESCRIPTION

A fuel cell module is typically made up of a number of fuel cellsconnected in series to form a fuel cell stack. The fuel cell module alsoincludes a suitable combination of associated structural elements,mechanical systems, hardware, firmware and software that is employed tosupport the function and operation of the fuel cell module. Such itemsinclude, without limitation, piping, sensors, regulators, currentcollectors, seals and insulators.

Referring to FIG. 1, shown is a simplified schematic diagram of a ProtonExchange Membrane (PEM) fuel cell module, simply referred to as fuelcell module 100 hereinafter, that is described herein to illustrate somegeneral considerations relating to the operation of fuel cell modules.It is to be understood that the present invention is applicable tovarious configurations of fuel cell modules that each include one ormore fuel cells.

There are a number of different fuel cell technologies, and in general,this invention is expected to be applicable to all types of fuel cells.Besides Proton Exchange Membrane (PEM) fuel cells, other types of fuelcells include, without limitation, Alkaline Fuel Cells (AFC), DirectMethanol Fuel Cells (DMFC), Molten Carbonate Fuel Cells (MCFC),Phosphoric Acid Fuel Cells (PAFC), Solid Oxide Fuel Cells (SOFC) andRegenerative Fuel Cells (RFC).

The fuel cell module 100 employs hydrogen as a fuel and air as a sourcefor an oxidant. Air is approximately 80% nitrogen (N₂) and 20% oxygen(O₂) and is thus a suitable source of the oxidant. These percentageshave been approximated ignoring the presence of other gases in theatmosphere (e.g. CO₂, CO, SO₂, PbS, etc.).

The fuel cell module 100 includes an anode electrode 21 and a cathodeelectrode 41. The anode electrode 21 includes a gas input port 22 and agas output port 24. Similarly, the cathode electrode 41 includes a gasinput port 42 and a gas output port 44. An electrolyte membrane 30 isarranged between the anode electrode 21 and the cathode electrode 41.

The fuel cell module 100 also includes a first catalyst layer 23 betweenthe anode electrode 21 and the electrolyte membrane 30, and a secondcatalyst layer 43 between the cathode electrode 41 and the electrolytemembrane 30. In some embodiments the first and second catalyst layers23, 43 are deposited on the anode and cathode electrodes 21,41,respectively.

A load 115 is coupled between the anode electrode 21 and the cathodeelectrode 41.

In operation, fuel comprising hydrogen is introduced into the anodeelectrode 21 via the gas input port 22 under some conditions. Examplesof the conditions include, without limitation, factors such as flowrate, temperature, pressure, relative humidity and a mixture of thehydrogen with other gases. The hydrogen reacts electrochemicallyaccording to reaction (1), given below, in the presence of theelectrolyte membrane 30 and the first catalyst layer 23.

H₂+2H⁺+2e⁻  (1)

The chemical products of reaction (1) are hydrogen ions (i.e. cations)and electrons. The hydrogen ions pass through the electrolyte membrane30 to the cathode electrode 41 while the electrons are drawn through theload 115. Excess hydrogen (sometimes in combination with other gasesand/or fluids) is drawn out through the gas output port 24.

Simultaneously an oxidant, such as oxygen in the air, is introduced intothe cathode electrode 41 via the gas input port 42 under someconditions. Examples of the conditions include, without limitation,factors such as flow rate, temperature, pressure, relative humidity anda mixture of the oxidant with other gases. The excess gases, includingun-reacted oxidant and the generated water are drawn out of the cathodeelectrode 41 through the gas output port 44.

The oxidant reacts electrochemically according to reaction (2), givenbelow, in the presence of the electrolyte membrane 30 and the secondcatalyst layer 43.

½O₂+2H⁺+2e⁻=H₂O   (2)

The chemical product of reaction (2) is water. The electrons and theionized hydrogen atoms, produced by reaction (1) in the anode electrode21, are electrochemically consumed in reaction (2) in the cathodeelectrode 41. The electrochemical reactions (1) and (2) arecomplementary to one another and show that for each oxygen molecule (O₂)that is electrochemically consumed two hydrogen molecules (H₂) areelectrochemically consumed.

Continuously supplying a fuel cell module (e.g. the fuel cell module 100illustrated in FIG. 1) with hydrogen fuel and oxidant to driveelectrochemical reactions (1) and (2) is wasteful and is unnecessary inmany situations, such as, for example, where there is a fluctuating orintermittent load. However, in some instances shutting down a fuel cellmodule initiates one or more undesired reactions that degrade somecomponents of the fuel cell module. Thus, it is desirable to be able toreliably turn-off (i.e. shutdown) and re-start a fuel cell modulewithout causing excessive degradation to some components of the fuelcell module. In some fuel cell modules 100 there is provided amodification that reduces the rate of wear and degradation experiencedby some components of the fuel cell module during shutdown andre-starting periods. In some fuel cell modules 100, the modification isadapted to passively reduce the rate of wear and degradation, whereas inother embodiments active mechanisms are employed to support passivereduction in the rate of wear and degradation. In particular, in somefuel cell modules 100 the rate of wear and degradation is reduced byreducing the amount of combustion of the remaining reactants whileincreasing the electrochemical consumption of those reactants during ashutdown process.

Referring to FIG. 2, shown is a schematic diagram illustrating a fuelcell module 300. Those skilled in the art will appreciate that a fuelcell module also includes a suitable combination of supporting elements,commonly referred to as ‘balance of plant’, which are not shown in FIG.2 but could be provided with the fuel cell module 300.

The fuel cell module 300 includes a fuel cell stack 200 that is made upof one of more PEM fuel cells. Each PEM fuel cell (not shown) includesan electrolyte membrane arranged between an anode electrode and acathode electrode as schematically illustrated in FIG. 1. The fuel cellstack 200 has a cathode inlet port 202, a cathode outlet port 203, ananode inlet port 204 and an anode outlet port 205. The cathode inlet andoutlet ports 202,203 are fluidly connected to each of the respectivecathode electrodes included in the fuel cell stack 200. Similarly, theanode inlet and outlet ports 204,205 are fluidly connected to each ofthe respective anode electrodes included in the fuel cell stack 200.

The fuel cell stack 200 also includes electrical connections 18 a,bacross which a load (e.g., an electric motor) is connectable. Arelatively small parasitic load 17 is optionally connected across theelectrical connections 18 a,b of the fuel cell stack 200. The smallparasitic load 17 helps to limit the voltage response during a shutdownprocess, which is described in more detail below.

The value of the parasitic load 17 is preferably chosen to be relativelysmall compared to an actual load (e.g. the electric motor) that the fuelcell module 300 supplies power to, so that the amount of powerdissipated by the parasitic load 17 during normal operation isrelatively small compared to the amount of power dissipated through theactual load. Optionally, the parasitic load 17 is chosen such that itdissipates less than 0.03% the amount of power dissipated by the actualload during normal operation.

In FIG. 2, the small parasitic load 17 is permanently coupled across theelectrical connections 18 a,b and thus, power is dissipated by the smallparasitic load 17 during normal operation. Optionally, the smallparasitic load 17 may be arranged so that it is coupled across theelectrical connections 18 a,b of the fuel cell stack 200 immediatelybefore or after the fuel cell module 300 is shutdown and is decoupledfrom the fuel cell stack 200 during normal operation.

Alternatively, the parasitic load 17 may be made-up of internalimpedances within the fuel cell stack 200. In particular, themembrane(s) included in the fuel cell stack 200 may provide enough of aninternal resistance to serve as an adequate parasitic resistance duringa shutdown process for limiting the voltage response of the fuel cellstack 200.

The fuel cell module 300 includes input valves 10 and 12 that arecontrollable to cut-off the inflow of reactant gases to the cathodeinlet port 202 and the anode inlet port 204, respectively. Similarly,output valves 11 and 13 are provided to controllably cut-off the outflowof exhaust gases from the cathode outlet port 203 and the anode outletport 205, respectively.

The input valve 10 is connected in series between the cathode inlet port202 and a blower 60. The blower 60 is any device (e.g., a motorized fan,a compressor, etc.) suitable to force air into the cathode inlet port202 when the valve 10 is open. Optionally, the blower 60 also serves topassively deter, but not necessarily stop, the free flow of air into thecathode inlet port 202 when power is cut-off from the blower 60. This isdescribed in more detail below with reference to FIGS. 3, 4 and 6.

The input valve 12 is connected in series between a fuel supply port 107and the anode inlet port 204. The fuel supply port 107 is furtherconnectable to a hydrogen fuel supply vessel (not shown) or some otherhydrogen fuel delivery system (not shown). A fuel reservoir 19 and aflow control device 14 are connected respectively in series between theinput valve 12 and the anode inlet port 204.

The output valve 11 is connected in series between the cathode outletport 203 and a first exhaust port 108. Similarly, the output valve 13 isconnected in series between the anode outlet port 205 and a secondexhaust port 109. The exhaust ports 108 and 100 are each optionallyconnectable to other devices, such as for example, an exhaust systemincluding an electrolyzer for re-cycling exhaust gases or liquids fromthe fuel cell module 300.

A check valve 15 is connected between an air supply port 106 to theambient environment (not illustrated) and the cathode inlet port 202,such that the check valve 15 is in parallel with the input valve 10.Optionally, the check valve 15 may be a pressure sensitive mechanismthat opens when the pressure at the cathode inlet port 202 drops belowthe air pressure of the ambient environment by a pre-set amount, knownas a cracking pressure. The cracking pressure may be set to correspondto a predetermined pressure differential between the air pressure in theambient environment and the pressure inside of the cathode inlet port202. The predetermined pressure differential may correspond to a totalvolume of a mixture of gases in the cathode electrodes in the fuel cellstack 200 and, in particular, to an amount of oxygen in the cathodeelectrodes relative to other gases, such as for example nitrogen fromthe air. This is described in further detail below with reference toFIG. 3.

The hydrogen reservoir 19 is provided to store a fixed amount ofhydrogen that is employed during a shutdown process of the fuel cellmodule 300 that is described in further detail below with reference toFIG. 3. Optionally, the hydrogen reservoir 19 may be a vessel that isappropriately sized to store enough hydrogen fuel to substantiallyelectrochemically consume the oxygen remaining in the fuel cell module300 when the valves 10, 11, 12 and 13 are closed and the forced inflowof air from the blower 60 is terminated. In another option, the hydrogenreservoir 19 is made-up of a predetermined length of hose or tubing(possibly coiled) for storing enough hydrogen for the same purpose.Alternatively, the hydrogen reservoir 19, whether in the form of avessel, hose or tubing, may be smaller than required but the amount ofhydrogen fuel in the hydrogen reservoir 19 is replenished as requiredduring a shutdown process so that enough hydrogen fuel is provided tosubstantially electrochemically consume the remaining oxygen. Moreover,those skilled in the art would appreciate that the amount of hydrogen(or reactant of interest) remaining in a fuel cell stack after shutdownis to be taken into consideration when sizing a hydrogen (reactant)reservoir. The amount of hydrogen to be provided is preferably alsoadjusted to account for the amount of air or oxygen, if any, that isexpected to flow into the fuel cell stack during the shutdown procedure,as will be further discussed below.

The flow control device 14 is provided to regulate the supply ofhydrogen fuel delivered to the anode inlet port 204 by, for example,setting the pressure of the hydrogen fuel delivered to the anode inletport 204. Optionally, the flow control device 14 may be a forwardpressure regulator that is dome loaded using air pressure in combinationwith a bias spring. The forward pressure regulator sets the pressure atthe anode inlet port 204 relative to the pressure at the cathode inletport 202 by some amount. For example, the pressure at the anode inletport 204 may be regulated to be higher than the pressure at the cathodeinlet port 202 by a predetermined fixed amount. Alternatively, a flowcontrol device may be used that requires a power supply for operation,whereas a flow control device may also be a passive element, such as forexample, a passive forward pressure regulator.

The fuel cell module 300 optionally includes a hydrogen recirculationpump 16 connecting the anode outlet port 205 to the anode inlet port204. During normal operation of the fuel cell module 300 the hydrogenrecirculation pump 16 is operable to re-circulate some portion of theunused hydrogen expelled through the anode outlet port 205 back to theanode inlet port 204.

Examples of the types of valves that are usable for the valves 10, 11,12 and 13 include, without limitation, normally closed valves, normallyopen valves and latching valves. Those skilled in the art wouldappreciate that various other types of valves may be suitably employed.

Optionally, some of the valves 10, 11, 12 and 13 may be normally closedvalves. A normally closed valve is opened, thus permitting free flow ofgases (or liquids), only when a control signal (or some electromotiveforce) is continuously supplied to the particular valve. That is, whenpower is not supplied to a particular normally closed valve, the valveremains closed, thus preventing the free flow of gases (or liquids)through the valve,

Optionally, some of the valves 10, 11, 12 and 13 may be normally openvalves. A normally open valve is closed, thus stopping the free flow ofgases (or liquids), only when a control signal (or some electromotiveforce) is continuously supplied to the particular valve. That is, whenpower is not supplied to a particular normally open valve, the valveremains open, thus allowing the free flow of gases (or liquids) throughthe valve.

Optionally, some of the valves 10, 11, 12 and 13 may be latching valves.A latching valve requires a control signal pulse to switch between“open” and “closed” positions. In the absence of a control signal pulse(or another electromotive pulse) a latching valve remains in theposition it is in without change.

During normal (i.e. energy producing or an on state) operation of thefuel cell module 300 the valves 10, 11, 12 and 13 are open permittingthe free flow of gases (and liquids) to/from the respective ports 202,203, 204 and 205. Moreover, power is supplied to the blower 60, the flowcontrol device 14 and the hydrogen re-circulation pump 16 to regulatethe inflows of reactant gases into the fuel cell stack 200. Thoseskilled in the art will appreciate that other supporting elements aresupplied with power accordingly and that energy produced by the fuelcell module 300 is coupled from the electrical connections 18 a,b.

Oxidant for the cathode electrodes in the fuel cell stack 200 isobtained from air, which, again, is made up of approximately 20% oxygen.The blower 60 forces air into the cathode inlet port 202 via the openinput valve 10. Once inside the cathode electrodes some of the oxygenfrom the air is employed in the electrochemical reaction (2) describedabove.

Hydrogen fuel travels through the fuel supply port 107 into the anodeinlet port 204 via the hydrogen reservoir 19 and the flow control device14. The hydrogen recirculation pump 16 also contributes to the hydrogenfuel supply delivered to the anode inlet port 204, as it operates toforce some portion of the unused hydrogen that is expelled from theanode outlet port 205 back into the anode inlet port 204. Once insidethe anode electrodes some of the hydrogen is employed in electrochemicalreaction (1) described above.

Excess exhaust gases and liquids from the cathode outlet port 203 andthe anode outlet port 205 flow through the corresponding output valves11 and 13 and out of the fuel cell module 300 through exhaust ports 108and 109, respectively.

The check valve 15 remains closed during normal operation since thepressure in the cathode inlet port 202 is equal to or greater than theair pressure of the ambient environment.

When a conventional fuel cell module is shutdown the conditions withinthe fuel cell stack change. The conditions change because elements thatsupport and regulate the operation of the fuel cell stack switch totheir respective shutdown states. For example, the input and outputvalves are closed, which cuts off the supply inflows and exhaustoutflows. Moreover, when an element such as a flow control deviceswitches to a shutdown state internal conditions, such as for example,the pressure within the anode electrodes change. When the internalconditions of the fuel cell stack change the hydrogen and oxygenremaining in the fuel cell stack and the feed lines (between the fuelcell stack and the closed valves) are often substantially consumed incombustion reactions as opposed to being consumed in the electrochemicalreactions (1) and (2), as described above.

The fuel cell module 300 illustrated in FIG. 2 is not a conventionalfuel cell module, as the components of the fuel cell module 300 areconfigured to passively reduce the overall amount of combustion ofhydrogen and oxygen within the fuel cell stack 200 during a shutdownprocess. This is accomplished by passively inducing an increase in theelectrochemical consumption of hydrogen and oxygen that is left insidethe fuel cell module 300 relative to what would normally occur during ashutdown process in a conventional fuel cell module.

In particular, the hydrogen reservoir 19 serves as a source for asufficient amount of additional hydrogen fuel for the fuel cell stack200 after the input valve 12 has been closed. Briefly, the additionalhydrogen fuel drawn from the hydrogen reservoir 19, in combination withother parts of the fuel cell module 300, induces the electrochemicalconsumption of the oxygen remaining inside the fuel cell stack 200.Also, since the source of the oxygen is air (which is approximately 80%nitrogen) the electrodes within the fuel cell stack 200 are passivelyblanketed with nitrogen. A high concentration of nitrogen reduces theamount of combustion that occurs within the fuel cell stack 200. Thepassive blanketing process is a function of the change in pressureswithin the fuel cell module 300 and specifically within the fuel cellstack 200. The blanketing process that occurs during a shutdown processis described in detail below with reference to FIG. 3 and continuedreference to FIG. 2.

FIG. 3 shows a chart illustrating an approximate and simplifiedbreakdown of the mixture of gases present in the cathode electrodes ofthe fuel cell stack 200 shown in FIG. 2 during sequential stages of ashutdown period. FIG. 3 is provided only as an aid for the visualizationof a substantially continuous and fluid process and it is in no wayintended to limit the scope of the invention as claimed in the followingsection.

When the fuel cell module 300 is shutdown the inflows of reactant gases(hydrogen fuel and oxygen carried in the air) are cutoff so that thefuel cell stack 200 is effectively starved of the reactant gases thatare needed to continue the electrochemical reactions (1) and (2). Inorder to do this, the valves 10, 11, 12 and 13 are closed and the powersupplied to the blower 60, the flow control device 14 and the hydrogenrecirculation pump 16 is cut-off. Closing the output valves 11 and 13reduces the amount of gases that leak into the cathode and anodeelectrodes, respectively, via the corresponding outlets 203 and 205,when the fuel cell module 300 is shut down.

The role of the parasitic load 17, whether it is connected permanentlyor not, is to limit the voltage of the fuel cell stack 200 (i.e. thestack voltage) when the fuel cell module 300 is shutdown and/orde-coupled from the actual load. If the parasitic load 17 is notconnected permanently, the parasitic load 17 is coupled across theelectrical connections 18 a,b immediately before or after a shutdownprocess is initiated. Preventing the output voltage of the fuel cellstack 200 from reaching a very high level helps to limit anelectrochemical corrosion mechanism that can be triggered by a highstack voltage. The presence of the parasitic load 17 further induces theelectrochemical consumption of the hydrogen and oxygen remaining withinthe fuel cell module 300 when a shutdown process is initiated.

Specifically, the parasitic load 17 passively induces theelectrochemical consumption of the remaining reactant gases by providinga path for current and voltage to be discharged from the fuel cell stack200. As the concentration of the reactant gases is reduced on either oneor both of the anode or cathode electrodes, the electrochemicalpotential of the constituent fuel cells (measured as voltage) of thefuel cell stack 200 decreases. If the parasitic load 17 is a simpleresistor, as the fuel cell voltage decreases, the corresponding currentflowing through the resistor also decreases. This coupling between thegradual decrease in fuel cell voltage potential and the resultingdecrease in current dissipation from a static resistor results in agradual decrease in fuel cell voltage without the danger of fuel cellsgoing negative within the fuel cell stack, as would be the case if alarger current draw was occurring without sufficient supply of reactantgases.

Referring now to 3-1 in FIG. 3, immediately after a shutdown process isinitiated the cathode electrodes within the fuel cell stack 200 containa mixture of gases that roughly corresponds to the composition of air(on earth). That is, each cathode electrode in the fuel cell stack 200contains a mixture of gases that is approximately 80% nitrogen and 20%oxygen (ignoring traces of other gases). The pressure in each cathodeelectrode is approximately the same as the air pressure in the ambientenvironment (e.g. about 1 atm).

As the conditions within the fuel cell stack change (for reasonsdiscussed above) the oxygen in the cathode electrodes of the fuel cellstack 200 is primarily electrochemically consumed according toelectrochemical reactions (1) and (2). The required hydrogen fuel usedto sustain the electrochemical reactions (1) and (2) is supplied fromthe hydrogen reservoir 19. As the oxygen is consumed the volume of thegas mixture in the cathode electrodes drops significantly causing acorresponding drop in internal pressure within the cathode electrodes.Illustrated at 3-2 of FIG. 3 is an example of the breakdown of a mixtureof gases within the cathode electrodes after the oxygen has beensubstantially consumed. Nitrogen makes up approximately 98% of the gasespresent in the cathode electrodes and the pressure within the cathodeelectrodes is approximately 0.8 atm.

With continued reference to FIG. 2, since the internal pressure withinthe cathode electrodes of the fuel cell stack 200 falls below the airpressure of the ambient environment the check valve 15 opens, presumingthat the cracking pressure has been exceeded. Additional air flows intothe fuel cell module 300 via the air supply port 106 and the open checkvalve 15 leading to a new mixture of gases in the cathode electrodes.The check valve 15 closes when the pressure within the cathodeelectrodes rises to a level sufficient to close the check valve (takinginto consideration the tolerances of the check valve used), which willhappen after a sufficient amount of air enters the cathode electrodes.When a conventional check valve is used a spring will force the valve toclose once the pressure within the cathode electrodes has risen enoughthat a delta pressure is below the check valve cracking pressure.

Assuming that the check valve were to remain open until the pressurewith the cathode electrode was approximately equivalent to that of theambient environment, the breakdown of the new mixture of gases isillustrated at 3-3 of FIG. 3. The new mixture of gases consists of 80%nitrogen from the original mixture of gases illustrated at 3-1, and 20%of newly added air. Taking into consideration that air is about 80%nitrogen, the equivalent breakdown of the new mixture of gases shown at3-3 is illustrated at 3-4 of FIG. 3. The total amount of nitrogenpresent in the cathode electrodes is about 96% and the pressure is aboutthe same as the air pressure of the ambient environment (e.g. 1 atm).This process is repeated, with the oxygen present in the cathodeelectrode (being approximately 4% of the cathode electrode volume) beingelectrochemically consumed with hydrogen provided from the hydrogenreservoir 19. In turn, the void created in the cathode electrodes by theoxygen consumption would be filled with air from the ambient environment(once again composed of approximately 80% nitrogen and 20% oxygen).Consequently, the cathode electrodes of the fuel cell stack 200 areblanketed with predominantly nitrogen gas by this substantiallycontinuous process.

Furthermore, the arrangement of the fuel cell module 300 illustrated inFIG. 2 also induces passive nitrogen blanketing of the anode electrodesin the fuel cell stack 200. As the hydrogen fuel from the hydrogenreservoir 19 is consumed, the volume of the gas mixture present in theanode electrodes drops, which, subsequently results in a correspondingpressure drop within the anode electrodes. The pressure drop within theanode electrodes induces a pressure gradient to be established acrossthe respective membranes from the cathode to the anode side of eachmembrane in the fuel cell stack 200. This pressure gradient willpassively draw nitrogen across the membranes from the respective cathodeelectrodes to the anode electrodes, thus, causing the anode electrodesto be blanketed with nitrogen as well.

Those skilled in the art will appreciate that the blanketing of thecathode and the anode electrodes occurs in concert in a continuous andfluid manner and it is thus difficult to illustrate this process indiscrete steps. Thus, the description provided above is not intended tolimit the scope of the invention to a specific sequence of discreteevents or processes.

Optionally, a fuel cell module may be configured to actively reduce theoverall amount of combustion of hydrogen and oxygen within the fuel cellstack 200 during a shutdown process. For example, nitrogen from areservoir may be injected into the cathode electrodes, the anodeelectrodes, or both, of the fuel cell module during a shut down process.

Optionally, and in order to achieve a more effective blanketing of theanode and cathode electrodes with nitrogen of atmospheric pressure,sufficient access to additional air may be provided to as to leave ahigh concentration of nitrogen remaining after the oxygen has beenalmost completely consumed. This in turn requires a near stoichiometricamount of hydrogen to be supplied to the anode electrodes of a fuel cellstack to facilitate the electrochemical consumption of the oxygen. Moregenerally, at least one reactant supplied to a fuel cell must beprovided with a non-reactive agent that remains within the fuel cellafter the reactants have been almost completely electrochemicallyconsumed by one another.

Still referring to FIG. 3, some aspects of restarting the fuel cellmodule 300 can be considered. As discussed above, at 3-3 of FIG. 3, themixture of gasses in the cathode electrode 41 comprises about 4% oxygenand the fuel cell stack 200 has not been completely discharged by theparasitic load 17. If a need arises to re-start the fuel cell module atthis time, the input valve 12 and output valve 13 may be opened,momentarily or permanently, for example using electrical power from abattery provided with the fuel cell module 300, to allow hydrogen from apressurized fuel tank to displace the nitrogen in the anode electrode21. With some oxygen present within the cathode electrode 41, anelectrochemical reaction can commence and be used to assist the batteryin re-charging the fuel cell stack 200. Once the fuel cell stack 200 isre-charged, normal operation can be re-commenced. Further, afternitrogen has been drawn into the anode electrode 21, input valve 10 andoutput valve 11 may be opened. Over time, for example several hours, aday or more, air or oxygen will move by natural forces into the cathodeelectrode 41. If the fuel cell module 300 is started up in thiscondition, an electrochemical reaction is again available to helpre-charge the fuel cell stack 200. However, at 3-4 in FIG. 3, or near toit, very little if any oxygen is available in the cathode electrode 41and very little, if any, electrochemical reaction is available to helpre-charge the fuel cell stack 200. In this case, the fuel cell module300 may not restart quickly in the absence of an otherwise unnecessarilylarge battery used to re-charge the fuel cell stack.

Referring to FIG. 3B, at the beginning of a start up method, the cathodeelectrode 41 is at 3-5 blanketed almost entirely with nitrogen. In orderto decrease the start up time required, an amount of air is added to thecathode electrode, displacing some of the nitrogen as shown at 3-6.Oxygen in the air is now available for electrochemical reactions to helpcharge the fuel cell stack 200. The amount of air shown in 3-6 is onlyan example. The amount of air added to the cathode electrodes 41 of thefuel cell stack 200 before the fuel cell stack is recharged may be, forexample, 10% to 100% of the available gas volume in the cathodeelectrodes 41. The air is provided by a source of energy other than thefuel cell stack, for example a battery or pressurized gas.

The fuel cell stack 200 may be considered to be charged, re-charged, ornot discharged, when it reaches a selected level of charge. The selectedlevel of charge does not need to be as large as the normal operating ormaximum charge level of the fuel cell stack 200. For example, theselected level of charge may be 50% or 75% of the normal operating ormaximum charge level of the fuel cell stack 200. The selected chargelevel is preferably sufficient for the fuel cell stack 200 to power thebalance of plant. For example, the fuel cell stack 200 is preferablyable when charge to operate an air blower 60 described below through itsordinary operating circuit.

Referring to FIG. 2, a pump 300 is used to move air into the cathodeelectrodes 41 of the fuel cell stack 200 before the fuel cell stack 200is recharged. During a start up procedure, inlet valve 12 is opened toallow hydrogen pressurized in a tank to flow into fuel supply port 107.The hydrogen dilutes nitrogen in the anode electrodes 21 and alsodisplaces a piston 302 in a cylinder 304 in communication with the anodeinlet port 204. The opposite face of the piston 302 is in communicationwith the cathode supply port 202. Accordingly, the hydrogen pressurecauses the piston 302 to discharge a volume of air from the cylinder 304into the cathode electrodes 41 of the fuel cell stack 200. The cylinder304 is recharged with air during the next shut down procedure by openingvalve 306 while there is a partial vacuum in the anode electrode 21 (3-2in FIG. 3) which causes piston 302 to retract. Alternatively, in a fuelcell module in which a sufficient vacuum is not created (for example asin FIG. 4), a spring 308 may be used. The volume of reservoir 19 isadjusted to compensate for hydrogen added to the fuel cell stack 200when piston 302 retracts. Optionally, other pumping mechanisms may beprovided to use the pressure, pressure drop, or flow of hydrogen duringa start up procedure to move air into the fuel cell stack 200.

Referring to FIG. 4, shown is a schematic diagram illustrating a secondfuel cell module 302. Those skilled in the art will appreciate that afuel cell module also includes a suitable combination of supportingelements, commonly referred to as ‘balance of plant’, which are notshown in FIG. 4 but could be provided with the second fuel cell module302.

The fuel cell module 302 illustrated in FIG. 4 is similar to the fuelcell module 300 illustrated in FIG. 2. Accordingly, elements common toboth fuel cell modules 300 and 302 share common reference indicia. Thedifferences between the two fuel cell modules 300 and 302 are that thefuel cell module 302 does not include input valve 10, output valve 11,check valve 15 and air supply port 106. Further, fuel cell module 302uses a fan 400 rather than pump 300 to supply air to the fuel cell stack200 during a start up procedure.

The blower 60, illustrated in FIG. 4 is coupled to the cathode inletport 202 without a valve (e.g. input valve 10) arranged there between.The blower 60 is any device (e.g., a motorized fan, a compressor, etc.)that serves to force air into the cathode inlet port 202. The blower 60also serves to passively deter, but not necessarily stop, the free flowof air into the cathode inlet port 202 when power is cut-off from theblower 60. The blower 60 is designed or selected to operate at the fuelcell stack 200 voltage and is powered by the fuel cell stack 200 duringnormal operation of the second fuel cell module 302.

During normal operation, the fuel cell module 302 operates in asubstantially identical manner to fuel cell module 300 described above.

During a shutdown process the operation of the fuel cell module 302 issimilar to the operation of the fuel cell module 300; however, asalready noted, there is no check valve to deter and permit free air flowinto the cathode inlet port 202. Instead, the flow of air into thecathode inlet port 202 is slowed down enough by the path through theblower 60 that the oxygen remaining in the cathode electrodes of thefuel cell stack 200 (when the fuel cell module 300 is shutdown) issubstantially electrochemically consumed before additional air flowsinto the cathode electrodes to replace the lost volume of the consumedoxygen. That is, with further reference to FIG. 3, the breakdown of themixture of gases in the cathode electrodes is similar to what is shownat 3-2 before additional air is passively drawn into the cathodeelectrodes by the relative drop in pressure. Once additional air makesits way through the blower 60 into the cathode electrodes of the fuelcell stack 200 the breakdown in the mixture of gases in the cathodeelectrodes is similar to what is shown in 3-3 (and, equivalently 3-4).

In other words, the partial restriction of the air flow through theblower 60 prevents the continuous, rapid replenishment of theelectrochemically consumed oxygen on the cathode electrode which wouldprevent the formation of a predominately nitrogen rich gas compositionon the cathode electrode. Thus a gradual depletion of oxygenconcentration on the cathode electrode follows a similar process asdescribed above with respect to FIG. 2, with the exception that no largemeasurable vacuum is created in the cathode electrodes. Rather theelectrochemical depletion of oxygen creates a volumetric void and alocalized depleted oxygen concentration in the cathode electrodes thatdraws additional air to the electrode surface (through a combination ofpressure and concentration differential driving forces).

Moreover, since there is no output valve (e.g. output valve 11) to blockthe path from the cathode outlet port 203 to the first exhaust port 108,some air flows into the cathode electrodes via the cathode outlet port203 and the first exhaust port 108. Also, as described above withrespect to FIG. 2, as hydrogen is consumed, in the fuel cell module 302(of FIG. 4), the pressure in the anode electrodes drops causing nitrogento be drawn across the respective membranes.

It should also be noted that since valves 10 and 11 from FIG. 2 are notincluded in fuel cell module 302, air will continue to diffuse into thecathode electrode. Over time this will cause the gas composition in thecathode electrodes to equalize to approximately that of the surroundingatmosphere. This in turn will gradually result in a change inconcentration in the anode electrode gas composition, such that over anextended period of time it can be assumed that both the anode andcathode electrode gas compositions will be approximately that of thesurrounding atmosphere. In such embodiments slightly higher levels ofdegradation are expected compared to the previous examples describedabove.

Again, those skilled in the art will appreciate that the blanketing ofthe cathode and the anode electrodes occurs in concert in a continuousand fluid manner and it is thus difficult to illustrate this process indiscrete steps. Thus, the description provided above is not intended tolimit the scope of the invention to a specific sequence of discreteevents or processes.

As mentioned above, in the fuel cell module 302 the cathode electrodeseventually contain air after the fuel cell module 302 is shut down. Thismakes oxygen available to support electrochemical reactions to helpcharge the stack on start up. However, there is a period of time, whichmay range from five minutes to up to a day, after the fuel cell module302 is shut down but before air re-enters the cathode electrodes in anamount sufficient to provide a rapid start up. During this period oftime, the cathode electrodes are completely or partially blanketed withnitrogen, for example as in 3-5 of FIG. 3B, and start up time can bedecreased by forcing air into the cathode electrodes.

To move air into the cathode electrodes, a fan 400 is turned on untilthe fuel cell stack 200 is able to operate blower 60. Fan 400 may be,for example, a muffin fan of the type used to cool electronics. Fan 400is operable by way of a DC voltage supplied from a battery, for examplea battery used to operate valves 12, 13 and electronic controls for thefuel cell module 302. Operating fan 400 moves air into the cathodeelectrodes, for example as in 3-6 of FIG. 3A, to decrease the start uptime.

Optionally, fan 400 may be combined with other components of the fuelcell module 302. For example, fan 400 may be a second winding withinblower 60. Alternatively, fan 400 may be a flow sensor used duringnormal operation to measure the output of blower 60. Fan 400 may also belocated downstream of cathode outlet 203, or upstream of blower 60,rather than in the position between blower 60 and cathode inlet 202shown in FIG. 4. Fan 400 may also be located in parallel with blower 60,with or without an isolation valve, or in communication with aT-junction in a pipe connected to cathode inlet 202 or cathode outlet203, with or without an isolation valve.

Referring to FIG. 5, shown is a schematic diagram illustrating a thirdfuel cell module 304. Those skilled in the art will appreciate that afuel cell module also includes a suitable combination of supportingelements, commonly referred to as ‘balance of plant’, which are notshown in FIG. 5 but could be provided with the third fuel cell module304.

The fuel cell module 304 illustrated in FIG. 5 is similar to the fuelcell module 300 illustrated in FIG. 2. Accordingly, elements common toboth fuel cell modules 300 and 304 share common reference indicia. Thedifferences between the two fuel cell modules 300 and 304 are that thefuel cell module 304 does not include output valve 11, check valve 15and air supply port 106. Fuel cell module 304 also uses a fan 400 ratherthan a pump 300, however, fuel cell module 300 may alternatively use afan 400 and fuel cell module 304 may alternatively use a pump 306.

During normal operation the fuel cell module 304 operates in asubstantially identical manner to fuel cell module 300, described above.

During a shutdown process the operation of the fuel cell module 304 issimilar to the operation of the fuel cell module 302 described above.Again, there is no check valve to deter and permit free air flow intothe cathode inlet port 202. Moreover, the input valve 10 is arrangedbetween the blower 60 and the cathode inlet port 202, so additional aircannot flow into the cathode electrodes of the fuel cell stack 200 viathe blower 60 during a shutdown process since the input valve 10 isclosed. Instead, the flow of air into the cathode electrodes comesthrough the cathode outlet port 203 via the first exhaust port 108. Insuch an embodiment it is desirable to size and/or shape the firstexhaust port 108 such that the flow of air in the reverse direction isslowed down enough by the reverse path through the first exhaust port108 so that the oxygen remaining in the cathode electrodes of the fuelcell stack 200 (when the fuel cell module 300 is shutdown) issubstantially electrochemically consumed before additional air flowsinto the cathode electrodes to replace the lost volume of the consumedoxygen. That is, with further reference to FIG. 3, the breakdown of themixture of gases in the cathode electrodes is similar to what is shownat 3-2 before additional air is passively drawn into the cathodeelectrodes by the relative drop in pressure. Once additional air makesits way through the blower 60 into the cathode electrodes of the fuelcell stack 200 the breakdown in the mixture of gases in the cathodeelectrodes is similar to what is shown in 3-3 (and, equivalently 3-4).Also, as described above with respect to FIG. 2, as hydrogen isconsumed, in the fuel cell module 304 (of FIG. 5), the pressure in theanode electrodes drops causing nitrogen to be drawn across therespective membranes.

Again, those skilled in the art will appreciate that the blanketing ofthe cathode and the anode electrodes occurs in concert in a continuousand fluid manner and it is thus difficult to illustrate this process indiscrete steps. Thus, the description provided above is not intended tolimit the scope of the invention to a specific sequence of discreteevents or processes.

During the state up procedure, inlet valve 10 is opened before fan 400is turned on.

Referring to FIG. 6, shown is a schematic diagram illustrating a fourthfuel cell module 306 according to aspects of another embodiment of theinvention. Those skilled in the art will appreciate that a fuel cellmodule also includes a suitable combination of supporting elements,commonly referred to as ‘balance of plant’, which are not shown in FIG.6 but could be provided with the third fuel cell module 306.

The fuel cell module 306 illustrated in FIG. 6 is similar to the fuelcell module 300 illustrated in FIG. 2. Accordingly, elements common toboth fuel cell modules 300 and 306 share common reference indicia. Thedifferences between the two fuel cell modules 300 and 306 are that thefuel cell module 306 does not include input valve 10, check valve 15 andair supply port 106. Further, fuel cell module 306 is shown using a fan400 although it may also use a pump 300.

As in FIG. 4, the blower 60 illustrated in FIG. 6 is coupled to thecathode inlet port 202 without a valve (e.g. input valve 10) arrangedthere between. The blower 60 is any device (e.g., a motorized fan, acompressor, etc.) that serves to force air into the cathode inlet port202. The blower 60 also serves to passively deter, but not necessarilystop, the free flow of air into the cathode inlet port 202 when power iscut-off from the blower 60.

During normal operation the fuel cell module 306 operates in asubstantially identical manner to fuel cell module 300, described above.

During a shutdown process the operation of the fuel cell module 306 issimilar to the operation of the fuel cell modules 300 and 302; however,as already noted, there is no check valve to deter and permit free airflow into the cathode inlet port 202. Instead, the flow of air into thecathode inlet port 202 is slowed down enough by the path through theblower 60 that the oxygen remaining in the cathode electrodes of thefuel cell stack 200 (when the fuel cell module 300 is shutdown) issubstantially electrochemically consumed before additional air flowsinto the cathode electrodes to replace the lost volume of the consumedoxygen. That is, with further reference to FIG. 3, the breakdown of themixture of gases in the cathode electrodes is similar to what is shownat 3-2 before additional air is passively drawn into the cathodeelectrodes by the relative drop in pressure. Once additional air makesits way through the blower 60 into the cathode electrodes of the fuelcell stack 200 the breakdown in the mixture of gases in the cathodeelectrodes is similar to what is shown in 3-3 (and, equivalently 3-4).

Moreover, since the fuel cell module 306 includes the output valve 11,additional air is prevented from entering the cathode outlet port 203during a shutdown process since the output valve 11 is closed during theshutdown process. Also, as described above with respect to FIG. 2, ashydrogen is consumed, in the fuel cell module 306 (of FIG. 6), thepressure in the anode electrodes drops causing nitrogen to be drawnacross the respective membranes.

Again, those skilled in the art will appreciate that the blanketing ofthe cathode and the anode electrodes occurs in concert in a continuousand fluid manner and it is thus difficult to illustrate this process indiscrete steps. Thus, the description provided above is not intended tolimit the scope of the invention to a specific sequence of discreteevents or processes.

During the start up procedure, outlet valve 11 is opened before fan 400is turned on.

With reference to FIGS. 2, 4, 5 and 6, as an alternative for fuel cellmodules 300, 302, 304, 306 an optional second check valve 26(illustrated only in FIG. 6) can be coupled between the anode inlet port204 and the cathode inlet port 202. The second check valve 26 isconfigured to open when there is a pre-determined pressure differentialbetween the pressure in the anode electrode(s) and the cathodeelectrode(s) during a shutdown process permitting flow from only thecathode electrodes(s) to the anode electrode(s); and, during normaloperation the second check valve 26 is configured to remain closed.

The second check valve 26 is used to ensure that nitrogen from thecathode electrodes is passed to the anode electrodes when a sufficientportion of the hydrogen fuel from the hydrogen reservoir 19 is consumedelectrochemically, which will result in a corresponding pressure drop asdescribed above. This is to supplement and/or replace the need fornitrogen diffusion across the respective membranes in the fuel cellstack 200, as a means for blanketing the anode electrode(s).

With reference to FIGS. 4, 5 and 6, as an alternative for fuel cellmodules 302, 304, 306, the fan 400 may be omitted and its functionreplaced by an additional circuit for driving the blower 60 using abattery, for example a battery already present in the balance of plant.As mentioned above, blower 60 is driven during normal operation by thefuel cell stack. In this alternative, the battery is connected to blower60 to operate blower 60 as described for fan 400 during start-up. Thebattery is able to turn blower 60 only slowly, for example at less than25% or less than 10% of the normal operating speed of the blower 60. Thebattery may be connected to the blower through a transformer to providevoltage and current output more appropriate for moving the blower.Alternatively, the battery may be connected to the blower 60 through acircuit containing one or more capacitors configured to provide pulsesof electricity to the blower 60. The battery to blower circuit isswitched on at or near the beginning of the start-up procedure. After aperiod of time, optionally determined by polling the fuel cell stack 200to determine if the fuel cell stack 200 has is re-charged, the batteryto blower circuit is switch off and the fuel cell stack 200 iselectrically connected to the blower 60.

Optionally, though not preferably, the fuel cell stack 200 can be usedto drive fan 400 or blower 60, or assist the battery in driving fan 400or blower 60, before the fuel cell stack 200 is charged. This option isnot generally preferred because drawing power from the fuel cell stack200 delays re-charging the fuel cell stack 200 relative to an option inwhich the same amount of power is provided by a battery. However, thisoption may be useful in a case in which battery capacity is limited. Ifa fan 400 has as sufficiently low resistance, the benefit derived fromaccelerating chemical reactions in the fuel cell stack 200 may justifydrawing power from the fuel cell stack 200. If there is no fan 400, thefuel cell stack 200 can be connected to blower 60 through a start-upcircuit having one or more transistors or capacitors configured tosupply the blower 60 with pulsed or continuous power while reducing theapparent resistance of the blower 60 or otherwise restricting the powerdrawn from the fuel cell stack 200. In a further option, a start-upprocedure may have an initial period of time in which a fan 400 orblower 60 is driven by a battery followed by an intermediate period oftime in which fan 400 is electrically connected to the fuel cell stack200, or a blower 60 is electrically connected to the fuel cell stackthrough a power limiting circuit, without or without the battery alsobeing connected to the fan 400 or blower 60. This intermediate period oftime ends when the fuel cell stack 200 is recharged. The recharged statemay be determined by polling the fuel cell stack 200 to determine if ithas reached a specified charge level, for example 50% or more or 75% ormore of its normal operating charge or maximum charge. The fuel cellmodule 302, 304, 306 then resumes normal operation.

What has been described is merely illustrative of the application of theprinciples of the invention. Those skilled in the art would appreciatethat other arrangements are possible without departing from the scope ofthe present invention. It is therefore to be understood that within thescope of the appended claims, the invention may be practiced otherwisethan as specifically described herein.

1. A fuel cell module, for use with hydrogen as a first reactant andair, including oxygen as a second reactant and nitrogen as anon-reactive agent, the fuel cell module comprising: a fuel cell stackincluding at least one fuel cell, each fuel cell including an anodeelectrode, a cathode electrode and an electrolyte medium arrangedbetween the anode electrode and the cathode electrode, wherein duringnormal operation the anode electrode is provided with the first reactantand the cathode electrode is provided with air; a parasitic load that isconnectable across the anode and the cathode electrodes; a reactantreservoir in communication with the anode electrode; and, a pump, fan orblower, operable to supply air to the cathode electrodes (a) while thefuel cell stack is in a discharged state or (b) using a power sourceother than the fuel cell stack.
 2. A process for shutting down andrestarting a fuel cell, the fuel cell including a first electrode, asecond electrode and an electrolyte arranged between the first andsecond electrodes, wherein during normal operation the first electrodeis provided with a first reactant and the second electrode is providedwith a first mixture containing a second reactant and a non-reactiveagent, the process comprising: stopping inflow of the first reactantinto the first electrode; cutting-off power to supporting elements ofthe fuel cell; drawing current through a parasitic load connectableacross the first and second electrodes; providing an amount of a firstreactant for the electrochemical consumption of a remaining amount of asecond reactant; permitting an inflow of an amount of the first mixtureinto the second electrode; and, when re-starting the fuel cell module,providing a flow or amount of the first mixture to the second electrode(a) before the fuel cell stack is recharged or (b) using a power sourceother than the fuel cell stack.
 3. A fuel cell module comprising, a fuelcell stack; a device adapted to supply air to one or more cathodeelectrodes of the fuel cell stack (a) while the fuel cell stack is in adischarged state or (b) using a power source other than the fuel cellstack.
 4. The fuel cell module of claim 3 further comprising a batterywherein the device is operable by way of electrical energy provided bythe battery.
 5. The fuel cell module of claim 4 wherein the device is afan and the fuel cell module further comprises a blower adapted toprovide air to the one or more cathode electrodes when the fuel cellstack is operating in a charged state.
 6. The fuel cell module of claim5 wherein the fan is adapted to operate as a flow meter or flow sensorwhen the blower is operating.
 7. The fuel cell module of claim 3 furthercomprising a tank containing compressed hydrogen wherein the device isoperable by way of energy provided by flow, pressure or a change inpressure, of the hydrogen.
 8. The fuel cell module of claim 4 whereinthe device is a blower ordinarily powered by the fuel cell stack and thefuel cell module further comprises a circuit adapted to temporarilyconnect the battery to the blower.
 9. A process for starting a fuel cellmodule comprising a step of providing a flow of oxygen to a cathodeelectrode of a fuel cell stack (a) before the fuel cell stack isre-charged or (b) using a power source other than the fuel cell stack.10. The process of claim 9 wherein the cathode electrode has beenpreviously blanketed with a non-reactive agent.
 11. The process of claim9 wherein the flow of oxygen is provided by operating an electricaldevice driven by a battery.
 12. The process of claim 11 wherein theelectrical device is a fan other than a blower that is driven by thefuel cell stack during ordinary operation of the fuel cell module. 13.The process of claim 11 wherein the electrical device is a valve. 14.The process of claim 11 wherein the electrical device is a blower thatis driven by the fuel cell stack during ordinary operation of the fuelcell module.
 15. The process of claim 9 further comprising a step ofpolling the fuel cell stack to determine when the fuel cell stack isre-charged.
 16. The process of claim 15 wherein the fuel cell stack isconsidered to be re-charged when it has reached at least 50% of itsnormal operating or maximum state of charge.